The syndrome of juxtaglomerular hyperplasia, with hyperreninism, aldosteronism, hypokalemic alkalosis and normal blood pressure will be further investigated with special reference to magnesium metabolism. Plasma magnesium is frequently low in this and other syndromes showing hypokalemia. A defect in the function of the thick ascending limb of Henle's loop, where magnesium is actively reabsorbed, has been shown for Bartter's syndrome. This study is designed to examine the relationship between hypokalemia and hypomagnesemia in this syndrome and to explore the effect of high oral intake of magnesium on the plasma and urinary potassium and on the chloride clearance. Patients will be studied under constant metabolic conditions and balance will be assessed by measuring intake and output of magnesium and potassium with two dietary intakes (normal and high) of magnesium. Renal clearances under conditions which will induce maximal free water production will be performed to evaluate the renal handling of magnesium in relation to the renal handling of sodium, potassium and chloride in these patients with Bartter's syndrome. Agents which have been moderately effective in restoring the serum potassium towards normal in this syndrome will be combined with the increased magnesium intake and the same varibles will be measured. These agents will include aldactone, amiloride, triamterine and indomethacin.